The present invention relates to the fusion bonding of articles constructed of plastic, and more particularly to apparatus for performing multiple fusion bonds to join a plurality of workpieces to a fixed, relatively large and bulky workpiece.
Fusion bonding, also known as hot plate welding, is a well known technique for forming strong bonds between plastic members. Generally, the articles to be bonded are positioned spaced apart from one another with the surface portions to be bonded aligned and facing one another. A heating platen is interposed between the articles in contact with the surfaces to be bonded, thus to form a fused or plasticized layer in the plastic comprising the articles. Immediately after heating, the platen is withdrawn and the articles are brought together under pressure and allowed to cool, forming the fusion bond.
One particularly advantageous but challenging fusion bonding operation is the attachment of a tubular spout to a container, for example a gas tank in which the spout is to be employed as a filler spout for the tank. Previously, a bore was first formed in the container by drilling, then the spout secured to the container in a rim area about the bore. Under this approach, however, the gas tank or other container is subject to contamination in the form of plastic chips or shavings deposited during the drilling operation. This kind of contamination in a gas tank can cause damage to the vehicle. In accordance with an invention described in pending U.S. Pat. No. 4,872,935, filed Nov. 28, 1988, the contamination is virtually eliminated when the boring operation and platen heating operation are performed as a single step employing a single combination fusing and boring tool
While this approach was found to yield highly satisfactory results, there remained a need for a fixture to efficiently carry out the boring and fusion step in combination with the proper alignment and positioning of the workpieces to be bonded. There further remained a need to provide a system to effectively employ this approach for multiple fusion operations, at least some of the operations including forming bores, in which a plurality of comparatively small thermoplastic items are fusion bonded to a relatively large or bulky fixed thermoplastic article, for example the body of an automobile gas tank or a tub for an automatic washing machine.
Devices for handling thermoplastic articles in bonding operations are known. For example, U.S. Pat. No. 3,809,737 (Rogers et al) discloses a process for forming plastic T connections including a hollow conduit, in which a portion of the skin of the main line protrudes into the branch line to increase the strength of the bond between the main line and branch line members.
U.S. Pat. No. 4,083,671 (Niederst et al) discloses a device for producing molded articles from foamable plastics, employing reciprocatory and rotary motion. A double-acting cylinder, hingedly mounted to a lower platen and to an upper platen near a hinged axle, controls movement of the upper platen toward and away from the lower platen, and pivotal movement of the upper platen after it reaches the upper limit of its linear movement. Another device for molding foamable plastics is disclosed in U.S. Pat. No. 4,015,920 (Niederst et al). A bipartite mold is secured to two movable clamping plates. One of the clamping plates can move through at least an angle of 180 .degree. from a parallel disposition relative to the other clamping plate.
Therefore, it is an object of the present invention to provide a fixture movable with respect to a fixed thermoplastic article, for aligning both a thermoplastic attachment and a heating platen with respect to the thermoplastic container and for selectively positioning the heating tool between the attachment and container.
Another object of the invention is to provide a fixture having independent means for supporting and reciprocating a thermoplastic workpiece and a fusion heating tool, respectively.
Yet another object of the invention is to provide a system for performing multiple fusion bonding operations joining a plurality of thermoplastic attachments to a relatively large and bulky thermoplastic article, while maintaining the article stationary.